1. Field of the Invention
The present invention relates to technology for correcting displacement of a reticle (mask) used in lithography process. More specifically, the invention relates to a displacement correction apparatus, an exposure system, an exposure method and a displacement correction program.
2. Description of the Related Art
In a manufacturing process of semiconductors such as LSIs, lithography processes are performed a plurality of times. In general, in the lithography processes, reduction projection exposure is performed stepwise on a semiconductor wafer with an exposure apparatus, such as an aligner or a stepper using a reticle. In an inspection process after manufacturing of reticles, the absolute position of the shape and pattern of a reticle is measured so as to be standardized, and then the reticles are inspected.
However, the reticle is slightly curved in the XYZ directions. Therefore, when the curved reticle is fixed (adsorbed) on a reticle stage of the stepper by use of a vacuum chuck or the like, displacement is generated due to curvature of elements of the reticle. This displacement behaves like curved elements of a projection lens of the stepper.
Conventionally, in the inspection process after the manufacturing of reticles, the absolute position of a curved reticle, that is, a reticle in which the curved elements occur, has been measured. Therefore, secondary distortion, which occurs when the reticle with the curved elements is fixed on the reticle stage, has not been taken into consideration. Hence, especially in an exposure process where a plurality of reticles is used, errors remain attributable to the displacement of the reticles fixed on the reticle stage, thus manufacturing yield is reduced.